Due to recent advances in group III-based ultraviolet (UV) light emitting diode (LED) technology, interest in using UV LEDs for various applications, such as disinfection of medical tools, water purification, fluorescence spectroscopy, medical therapy, and the like, is increasing. In order to successfully utilize such devices, they need to be packaged and isolated from interaction with the outside environment to protect the electrical components of these devices. In addition, packaging solutions can provide a way to improve light extraction efficiency. For example, one approach for improving light extraction uses an index matching encapsulant (e.g., similar to the approach used for visible LEDs) in order to decrease the total internal reflection (TIR) from the device surfaces and, as a result, extract more light from the UV LED.
Typical epoxy resin materials used for visible LED encapsulation are not adequate for UV LEDs as the resins are not sufficiently transparent to UV radiation and quickly deteriorate under the UV radiation. An ideal encapsulant should be “stable.” In particular, the optical and physical properties of the encapsulant should not change during packaging, LED assembly, and during the operating lifetime of the LED. For example, an encapsulant should be resistant to heating during the LED assembly, such as during soldering a chip onto a printed circuit board or during a curing process. During the curing process, drying of the encapsulant can further induce stresses in the material. As a result, an encapsulant that is not prone to crack during the curing procedure can be selected.
Recently, UV transparent, and partially UV transparent fluoropolymers have become important materials for UV applications and can serve as moldable encapsulants for optoelectronic devices. For instance, one approach discloses materials and methods used to package and encapsulate UV and deep UV (DUV) LEDs having emission wavelengths from around 360 nm to around 200 nm. The UV/DUV LED die, or its flip-chip bonded subassembly, are disposed in a low thermal resistance packaging house. Either the whole package or just the UV/DUV LED is globed with a UV/DUV transparent dome-shape encapsulation. This protects the device, enhances light extraction, and focuses the light emitted. The disclosure describes dome-shape encapsulation may be comprised of optically transparent PMMA, fluorinated polymers or other organic materials. Alternatively, it might be configured to include a lens made from sapphire, fused silica, or other transparent materials. The lens material is cemented on the UV/DUV LED with UV/DUV transparent polymers.